Characterization of cAMP-dependent inhibition of LPS-induced TNFα production by rolipram, a specific phosphodiesterase IV (PDE IV) inhibitor

Abstract

Bacterial endotoxins (lipopolysaccharide or LPS) provoke shock and tissue injury by eliciting the release of toxic factors from reticuloendothelial cells. One of the principal endogenous factors involved in this process is tumor necrosis factor alpha (TNFα). In this study, inhibitors selective for different classes of phosphodiesterases (PDE), were examined for their effects on LPS-induced TNFα production by human monocytes. The selective cAMP-PDE IV inhibitors, rolipram and RO-20-1724 were capable of inhibiting LPS-induced TNFα production by human monocytes in a concentration-dependent manner. Rolipram was used to examine further the cellular pharmacology of PDE IV inhibitors on cytokine production. The IC 50 for inhibition of LPS-induced TNFα production by rolipram was 0.1 μM, whereas production of IL-1β or IL-6 was unaffected. Furthermore, rolipram was equally effective in inhibiting TNFα production by a number of other stimuli. Inhibition of TNFα production by rolipram was associated with an elevation of intracellular cAMP, consistent with a mechanism involving phosphodiesterase inhibition. Rolipram was efficacious in suppressing LPS-induced TNFα mRNA expression, and at the protein level was also active when added to cultures post-stimulated with LPS. This indicates that rolipram may act at both the transcriptional and translational levels. Rolipram inhibited TNFα production in vivo in a rat endotoxemia model. Collectively, these data suggest that the phototypic inhibitor of PDE IV isozyme, rolipram, can effectively and selectively inhibit LPS-induced TNFα production through elevation of intracellular cAMP.